Hitherto, development of portable terminals (mobile terminals) which are provided with an apparatus for calculating a movement path (walking path) of a user by using autonomous navigation has been advanced (refer to Japanese Unexamined Patent Application Publication No. 11-194033).
Such an apparatus has, for example, a direction detecting function to detect a movement direction, a number-of-steps detecting function to detect a number of steps, a movement-distance calculating function to calculate a movement distance from the number of steps and a one step length that is input in advance, and a position detecting function to acquire an absolute position of a present location by using, for example, a global positioning system (GPS) receiver. The apparatus calculates a movement path of a user based on the values (the absolute position, the direction, the movement distance, etc.) acquired by using the above functions.
In addition, advanced safety services have received attention in recent years. The advanced safety services locate positions of vehicles on roads to provide information, warning, intervention control, etc. for the vehicles based on the located positions.
For example, position locating technologies using optical beacons provided on roads and optical beacon receivers which are in-vehicle devices are disclosed. The use of such a technology enables a vehicle to receive, for example, a stop warning service at an intersection at a time when the vehicle passes below an optical beacon provided before the vehicle enters the intersection (refer to Japanese Unexamined Patent Application Publication No. 2009-19979, and Japanese Unexamined Patent Application Publication No. 2009-26056).
However, since the number-of-steps measuring function in the related art can cause an error in the number of steps, the number of steps that is counted can be larger than or smaller than the actual number of steps. In addition, since the step length is set by the user, the difference in the step length can occur between the set step length and the actual step length.
In order to resolve above problems, methods for calculating accurate step lengths are disclosed. For example, Japanese Unexamined Patent Application Publication No. 09-89584 discloses a method of calculating a distance between two GPS measured values and dividing the distance by the number of steps to calculate an accurate step length. However, since a measurement error can occur in the GPS and an error in the number of steps can also occur, as described above, it may be difficult to calculate the accurate step length with the above technology.
In the related art, when a terminal is inclined, the inclination of the terminal is corrected to calculate an accurate azimuth by using direction detecting functions (refer to Japanese Unexamined Patent Application Publication No. 08-278137 and Japanese Unexamined Patent Application Publication No. 2004-286732). However, if the direction depicted by the terminal (the reference direction of the terminal) is different from the movement direction of a user carrying the terminal (for example, if the user advances while carrying the terminal that is transversely situated), it is not possible to correct the difference in the direction. As a result, a difference (direction difference) can occur between the direction measured by the terminal and the actual direction.
Furthermore, values measured by the GPS are directly used as the absolute positions in the autonomous navigation in the related art. The absolute positions are revised by calculating a distance corresponding to the measurement error because the measurement error is highly possible to occur in the GPS, as described above. In addition, various services including a service (right-turn assistance service) for depicting a timing to change a lane on a road when a vehicle is to turn right on the road, are proposed in the advanced safety services in vehicles. However, in order to realize the right-turn assistance service or the like, it is necessary to determine which lane the vehicle is on, whether the vehicle enters an intersection in which the vehicle is located, and so on.
The object and advantages of the embodiment discussed herein will be realized and attained by means of elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed and the following detailed description are exemplary and only are not restrictive exemplary explanatory are not restrictive of the invention, as claimed.